Mid and Deep Circulation in the Japan Sea

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The Japan Sea is a mini ocean and a very good test basin for the numerical ocean prediction. However, so far, the intermediate and deep circulation haven't been well understood. We carried out 4 cruises to survey the circulation below the surface layr during two fiscal years (1994,1995) as international cooperative field researches between Japan, Korea nad Russia.The CTD and chemistry measurements during the summer cruise in the main part of the Japan Sea (1994,7.5-7.25) showed the increase of the temperature in the deep layr with the rate of 0.02 C per 10 years and the oxgen decrease, suggesting no formation of the deep water during at least last ten years. Strong mesoscale activities with the time scale of month and the velocity exceeding 20 cm/s were detected in the deep Japan Basin by analyzing the recovered long-term (1993.8-1994.8) current mooring data. Many informations about the distribution of the salinity minimum layr with the oxgen maximum were obtained in this cruise.The second winter cruise (1996.2.15-2.25) carried out off Vladivostok in '96 winter detected the deep convection reaching 600m depth, while no sign of deep convection could be found in the first winter cruise (1995.3.1-3.15), because the winter in 1995 was warm.The ADCP and CTD measurements carried out during the summer cruise off the wakasa bay (1995.5.26-6.8) observed the subsurface counter current below the nearshore branch of the Tsushima current over the continental shelf break with the speed exceeding 10 cm/s. The presence and the structure of this undercurrent correspond well to the results of several numerical models.Many new aspects about the intermediate and deep clrculation found in this research will contribute much to the future studies for the Japan Sea circulation.